Field of the Invention
The present invention relates to a variable valve apparatus for an internal combustion engine.
Description of the Related Art
Conventionally there is well known a mechanism or an apparatus that varies a lift amount of an engine valve. WO2014/030226 discloses an example of an apparatus that varies a projecting amount of a cam in a cam shaft. This apparatus is provided with a cam base member rotated by a drive force from a crankshaft and a cam lobe member swingably connected to the cam base member. The cam lobe member is selectively positioned in any one of a retracting position of being stored in the cam base member and a projecting position of projecting radially outside from the cam base member according to an operating state of a hydraulic system. In the apparatus according to WO2014/030226, the lift amount of the engine valve is varied with this structure.
Here, an explanation will be made of the movement of a cam lobe member 102 to a cam base member 104 in the apparatus according to WO2014/030226 with reference to FIGS. 1A and 1B. FIG. 1A illustrates an example where the cam lobe member 102 is in the projecting position, and FIG. 1B illustrates an example where the cam lobe member 102 is in the retracting position. The cam lobe member 102 is regularly urged toward the projecting position by a spring (unillustrated). For regulating the projecting amount (that is, a swing range) of the cam lobe member 102 by the urging of the spring, a stopper pin 106 fixed in the cam lobe member 102 is arranged to be movable in a guide groove (elongated hole) 108 of the cam base member 104 along the longitudinal direction of the guide groove.
When supply of oil to a path upstream of a pin acting on the cam lobe member 102 is stopped not to apply a predetermined hydraulic pressure to the pin and the cam lobe member 102 is fixed in the projecting position to the cam base member 104, the cam lobe member 102 presses a rocker arm, thereby making it possible to open a valve (refer to a solid line in FIG. 2A). On the other hand, the oil is supplied to the path upstream of the pin acting on the cam lobe member 102 to apply the predetermined hydraulic pressure to the pin. Therefore when the cam lobe member 102 is fixed in the retracting position to the cam base member 104, the valve is not subjected particularly to a force in the opening direction (refer to a dotted line in FIG. 2A). This is because an outer surface of the cam base member 104 in FIGS. 1A and 1B has a shape based upon a reference circle. When the position of the cam lobe member 102 is changed from the projecting position to the retracting position, the hydraulic pressure is applied to the pin. In reverse, when the position of the cam lobe member 102 is changed from the retracting position to the projecting position, the hydraulic pressure applied to the pin is released.
When the hydraulic pressure applied to the pin is released, as long as the cam lobe member 102 does not become in the fixed state, the cam lobe member 102 continues to swing to the cam base member 104. FIG. 2B conceptually expresses the movement of the stopper pin 106 (that is, the movement of the cam lobe member 102) at the time the camshaft is rotating in a state where the cam lobe member 102 is not fixed. In a graph of FIG. 2B, the movement of the stopper pin 106 is expressed by a lost angle. The lost angle α, as illustrated in FIG. 1B, corresponds to a rotating angle of the stopper pin 106 around a swing center (center of a supporting point member 110) of the cam lobe member 102 to the cam base member 104. The lost angle α is, as illustrated in FIG. 1A herein, defined as zero when the cam lobe member 102 is in the projecting position, and to be the larger as the position of the cam lobe member 102 comes closer to the retracting position.
As schematically illustrated in FIG. 2B, when the cam lobe member 102 is not fixed by the lock pin, the lost angle preferably changes as illustrated in the solid line. However, when the urging force of the spring is insufficient, in some cases a steep movement of the cam lobe member 102 immediately before the cam lobe member 102 reaches the projecting position, that is, in the latter part of the swinging movement cannot be realized by the urging force of the spring. In this case, the contact between the cam lobe member 102 and the rocker arm is once lost, and thereafter, the cam lobe member 102 reaches the projecting position. As a result, the stopper pin 106 collides with one end 108a of the guide groove 108 in the longitudinal direction in a speed faster than a ramp speed originally set (refer to the dotted line in FIG. 2B). Such collision between the members emits a collision noise when the internal combustion engine is operating in a low rotation (for example, in an idling operation), which is desired for an improvement.
Therefore an object of the present invention is to provide a variable valve apparatus for an internal combustion engine that can suppress a rapid movement of a cam lobe member to a cam base member.